The present invention relates to a fuel supply apparatus for in-cylinder injection engines, and more particularly to a delivery flow rate control method.
One conventional fuel supply apparatus is known to perform the delivery flow rate control by giving a drive signal to an actuator for every delivery stroke and controlling a drive signal application timing, as described in, for instance, International Publication No. WO 00/47888.
The conventional high-pressure fuel pump described above, however, has a problem that there is a time lag from applying the drive signal to driving the actuator and, when a reciprocating cycle of a plunger is short, the operation of the actuator cannot keep up with the reciprocating action of the plunger.
In actual automobiles, such a situation can occur when the engine revolution speed is high. In apparatus that supply fuel to engines of large displacements, a similar situation also occurs when the number of reciprocations of the plunger during each rotation of a cam, i.e., the number of lobes of the drive cam, is increased to increase the delivery flow from the high-pressure fuel pump for every one revolution of the cam.
An object of the present invention is to provide a fuel supply apparatus for variable displacement, high-pressure fuel pumps, which enables a delivery flow rate control even when a reciprocating cycle of a plunger is short, without having to increase the responsiveness of an actuator, or a variable displacement mechanism.
The above object can be achieved by a fuel supply apparatus which comprises a high-pressure fuel pump of a single-cylinder plunger type having a variable displacement mechanism, the variable displacement mechanism supplying fuel under pressure to fuel injection valves, and a controller for controlling the variable displacement mechanism of the high-pressure fuel pump to regulate a fuel supply pressure, wherein the variable displacement mechanism is driven once at every two or more reciprocating motions of the plunger of the high-pressure fuel pump.
The above object is also achieved by the fuel supply apparatus wherein the pump does not deliver fuel in one of every two reciprocating motions thereof and controls a delivery flow in the other reciprocating motion.
The above object is also achieved by the fuel supply apparatus wherein the pump delivers all the volume of fuel displaced by the plunger in one of every two reciprocating motions thereof.
The above object is also achieved by the fuel supply apparatus wherein the controller calculates a necessary amount of fuel to be supplied to the fuel injection valves such that (i) when the amount of fuel to be supplied is nearly 50% or less of the maximum delivery flow rate of the high-pressure fuel pump, the pump does not deliver fuel in one of every two reciprocating motions thereof and controls a delivery flow in the other reciprocating motion, and (ii) when the amount of fuel to be supplied is nearly 50% or more of the maximum delivery flow rate of the high-pressure fuel pump, the pump delivers all the volume of fuel displaced by the plunger in one of every two reciprocating motions thereof and controls a delivery flow rate in the other reciprocating motion.
The above object is also achieved by a method of controlling a fuel supply apparatus, the fuel supply apparatus comprising a high-pressure fuel pump of a single-cylinder plunger type having a variable displacement mechanism, the variable displacement mechanism supplying fuel under pressure to fuel injection valves, a controller for controlling the variable displacement mechanism of the high-pressure fuel pump to regulate a fuel supply pressure at an almost constant value, and an actuator forming the variable displacement mechanism and effecting drive responsiveness to a drive signal given from the controller, wherein the variable displacement mechanism performs a variable displacement operation by changing its own position, and the controller, after having shut off the drive signal to the variable displacement mechanism, reduces the number of times of driving the variable displacement mechanism as compared with the number of reciprocating motions of the plunger so that the controller will not send the next drive signal at least until the variable displacement mechanism returns to its initial position.
The above object is also achieved by a method of controlling a fuel supply apparatus, the fuel supply apparatus comprising a high-pressure fuel pump of a single-cylinder plunger type having a variable displacement mechanism, the variable displacement mechanism supplying fuel under pressure to fuel injection valves, and a controller for controlling the variable displacement mechanism of the high-pressure fuel pump to regulate a fuel supply pressure at an almost constant value, wherein the high-pressure fuel pump has a suction valve automatically opening irrespective of the operation of the variable displacement mechanism, and the controller calculates a necessary amount of fuel to be supplied to the fuel injection valves such that (i) when the amount of fuel to be supplied is nearly 50% or less of a maximum delivery flow rate of the high-pressure fuel pump, the variable displacement mechanism is drive once so that the plunger does not deliver fuel in one of every two reciprocating motions thereof and controls a delivery flow in the other reciprocating motion, and (ii) when the amount of fuel to be supplied is nearly 50% or more of the maximum delivery flow rate of the high-pressure fuel pump, the variable displacement mechanism is driven once so that the plunger delivers all the volume of fuel displaced by the plunger in one of every two reciprocating motions thereof and controls a delivery flow rate in the other reciprocating motion.